OBJECTIVES: To continue our program of measurements of thermodynamic properties (partial molal free energies, enthalpies, and entropies) of solution for selected compounds expected to model the phenomenon of hydrophobic bonding. These will include, but not be limited to, solutions of the permanent gases. The measurements will take place in both water and heavy water and will cover the approximate temperature range 0-60 degrees C. Second we will interpret the data so obtained within the framework of the theory of isotope effects in condensed phase systems and employ it to refine currently accepted models of aqeuous solution structure. METHODS: The techniques we propose to employ include differential capacitance manometry, isothermal and adiabatic solution calorimetry, and freezing point depression and boiling point elevation measurements using quartz crystal thermometry. We have extensive experience with all of these techniques.